Where data is programmed in a NAND flash, a frequency of reading individual pieces of the data varies from each other. Some data is read frequently by the host, such as a popular video data server. Furthermore, map data between physical addresses used internal to the flash and logical addresses used external to the flash is read frequently by firmware in truly random read cases, such as an application in an enterprise data center. The frequently read host data and map data are referred to as hot read data.